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hash.h
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hash.h
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#pragma once
#include <cstddef>
#include <functional>
namespace prometheus {
namespace detail {
/// \brief Combine a hash value with nothing.
/// It's the boundary condition of this serial functions.
///
/// \param seed Not effect.
inline void hash_combine(std::size_t*) {}
/// \brief Combine the given hash value with another object.
///
/// \param seed The given hash value. It's a input/output parameter.
/// \param value The object that will be combined with the given hash value.
template <typename T>
inline void hash_combine(std::size_t* seed, const T& value) {
*seed ^= std::hash<T>{}(value) + 0x9e3779b9 + (*seed << 6) + (*seed >> 2);
}
/// \brief Combine the given hash value with another objects. It's a recursion。
///
/// \param seed The give hash value. It's a input/output parameter.
/// \param value The object that will be combined with the given hash value.
/// \param args The objects that will be combined with the given hash value.
template <typename T, typename... Types>
inline void hash_combine(std::size_t* seed, const T& value,
const Types&... args) {
hash_combine(seed, value);
hash_combine(seed, args...);
}
} // namespace detail
} // namespace prometheus